An ECG refers to a record of action current attributable to the contraction of the heart using a curve, and is an abbreviation for an electrocardiogram.
Since the excitation of the heart muscle first occurs in the sinus venosus and proceeds toward the auricle and the cardiac ventricle, the action current of the heart is depicted on a graph when the excitation is introduced from two arbitrary points to an ammeter (electrocardiograph).
A diagram, in which action potentials, which are generated by electric excitation that occurs when the heart muscle contracts, are transferred to the surface of a human body and waveforms caused by the current are depicted, is an ECG. This ECG is very important in the diagnosis of heart diseases.
In this diagram, in the case where the indicator needle of an ammeter draws an upward curve when the base portion of the heart is excited and becomes electrically negative with respect to the tip portion, the portions projected from an equipotential line are denoted by P, Q, R, S, T and U waves, according to the W. Ainthoben's nomenclature.
In order to obtain an ECG for the diagnosis of heart diseases, ECG methods using standard limb induction based on both hands (first induction: Lead I), a right hand and a left foot (second induction: Lead II), and a left hand and a left foot (third induction: Lead III) are used, as illustrated in FIG. 1. In addition, there are ECG methods using unipolar induction and chest induction.
The taking of ECGs is widely used in the diagnosis of coronary diseases, such as angina pectoris and myocardial infarction, arrhythmia, and electrolyte disorders, in the examination and determination of whether a disorder of the heart exists during an operation, and is important in the diagnosis of heart diseases.
Such an ECG is based on some biosignal, other than a biosignal related to an electromyogram, a brain wave, or a bio-impedance signal. The biosignal related to the ECG is a signal that is fundamental to the diagnosis of the health condition of an examinee and that uses a non-invasive method. The biosignal related to an ECG is widely used in clinical practice, along with a respiration signal.
In a medical field requiring the measurement of biopotentials, such as those for an ECG, an electromyogram and an electroencephalogram, to perform appropriate treatment, a method of transmitting electric signals from a body to an external device and making a diagnosis has been recently commercialized.
A conventional apparatus for taking ECGs, as illustrated in FIG. 2, includes a conductive fiber electrode 100 and an ECG amplifier 200. The conductive fiber electrode 100 includes three conductive fiber patches 101 and 101′ that are attached to the mattress of a bed.
The conductive fiber electrode 100 is formed by coating a polyester filament with copper and nickel, and is configured to conduct electricity.
For an examinee to have an ECG taken, the examinee wears clothes, including an upper garment allowing the chest or shoulders to be exposed to the outside, and knee pants, and lays himself or herself on a bed so that his or her back or shoulders come into contact with the two conductive fiber patches 101 provided on one side of the bed and his or her feet come into contact with the one conductive fiber patch 101′.
After the examinee's parts have come into contact with the conductive fiber patches 101 and 101′ as described above, the examinee's ECG is taken by the ECG method using Lead I, II or III through an ECG amplifier, as described in conjunction with FIG. 1.
A conventional apparatus for taking ECGs in an unnoticeable and unrestrictive manner is disclosed in Ishijima's thesis: Masa Ishijima, ‘Monitoring of ECGs in Bed Without Utilizing Body Surface Electrodes’, IEEE Transactions on Biomedical Engineering, Vol 40, No 6, June 1993, p 593-594. This apparatus is disadvantageous in that the surface of a body must be brought into contact with electrodes exposed on a bed because an ECG is taken directly on the surface of the examinee's body, so that the examinee must put on and take off clothes to have an ECG taken, which may be unpleasant for the examinee.
Furthermore, the conventional ECG apparatus and method have limitations in that it is not easy to repeatedly have an ECG taken at home using the ECG apparatus and method used in medical institutions, and it is inconvenient for unskilled persons to use the ECG apparatus. Moreover, the conventional ECG apparatus and method has a problem in that, when an examinee has an ECG taken using the conventional ECG apparatus and method, the examinee is aware that an ECG is being taken, so that it is difficult to obtain accurate ECG values.